WDPN32 PGTW 270300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (NINETEEN) WARNING 
NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.1N 145.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 457 NM SOUTH-SOUTHEAST OF IWO TO
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM 19W WITH A LOW-LEVEL CIRCULATION (LLCC) CENTER THAT HAS
BECOME MORE EXPOSED OVER THE PAST 6 HOURS WITH CONVECTION CONFINED
TO THE SOUTHERN PERIPHERY. THE SYSTEM HAS AN OVERALL ELONGATED
APPEARANCE AND WIND FIELD WITH A NORTHWEST TO SOUTHEAST
ORIENTATION. ENVIRONMENTAL ANALYSIS INDICATES THAT 19W IS IN A
MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE
EQUATORWARD OUTFLOW ALOFT, LOW (10-15 KTS) VERTICAL WIND SHEAR, AND
WARM SEA SURFACE TEMPERATURES OFFSET BY THE PRESENCE OF DRY AIR IN
THE WESTERN AND NORTHWESTERN SECTORS. THE DRY AIR SEEMS TO BE
HINDERING CONVECTIVE DEVELOPMENT IN THOSE AREAS. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE PARTIALLY
EXPOSED LLCC IN THE ANIMATED MSI. THE INITIAL INTENSITY OF 35 KTS
IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK
ESTIMATES AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST.  

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 36 KTS AT 270000Z
   CIMSS ADT: 39 KTS AT 270000Z
   CIMSS AIDT: 37 KTS AT 270000Z
   CIMSS DPRINT: 34 KTS AT 270040Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: DRY AIR TO THE WEST AND NORTHWEST

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: 19W IS FORECAST TO CONTINUE TRACKING
NORTHWESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF THE STR TO THE
NORTHEAST THROUGH TAU 48. BETWEEN TAU 48 AND 72, 19W IS FORECAST TO
TRACK MORE NORTHWARD AS IT BEGINS TO ROUND THE RIDGE AXIS. NEAR TAU
72, THE SYSTEM IS EXPECTED TO TURN NORTHEASTWARD AS IT TRACKS ALONG
THE NORTHWESTERN PERIPHERY OF THE STR. IT WILL THEN CONTINUE THAT
TRACK THROUGH THE REMAINDER OF THE FORECAST AND WILL BEGIN
INTERACTING WITH THE BAROCLINIC ZONE AROUND TAU 96 WITH
EXTRATROPICAL TRANSITION COMPLETED BY TAU 120. REGARDING INTENSITY,
19W IS EXPECTED TO REMAIN AROUND 35 KTS THROUGH TAU 36. THIS IS DUE
TO A COUPLE REASONS, THE FIRST BEING THE POSITION RELATIVE TO A
TUTT CELL TO THE NORTHEAST. THE TUTT CELL IS EXPECTED TO PROPAGATE
WESTWARD AND BE NEARLY ON TOP OF THE SYSTEM AROUND TAU 36. THIS WILL
HINDER DEVELOPMENT THROUGH INCREASED VERTICAL WIND SHEAR AND
RESTRICTED OUTFLOW ALOFT. THE SECOND REASON IS THAT THE DRY AIR
WILL CONTINUE TO INFRINGE ON THE CIRCULATION THROUGH TAU 36. AFTER
TAU 36, THE TUTT IS EXPECTED TO HAVE MOVED WESTWARD OF THE SYSTEM
AND THE ENVIRONMENT WILL MOISTEN, ALLOWING INTENSIFICATION TO
BEGIN. THE POSITION OF THE TUTT VARIES BETWEEN MODELS WITH ECMWF
SHOWING THE TUTT MOVE MUCH MORE SLOWLY, AND ALMOST FOLLOW 19W
NORTHEASTWARD. THIS SCENARIO WOULD HINDER DEVELOPMENT FOR A LONGER
PERIOD. THE JTWC FORECAST SITS CLOSER TO THE GFS SCENARIO WITH
STEADY INTENSIFICATION TO 60 KTS AROUND TAU 96. AFTER TAU 96,
VERTICAL WIND SHEAR IS EXPECTED TO INCREASE AS THE SYSTEM ENTERS
THE BAROCLINIC ZONE AND WILL WEAKEN TO AROUND 45 KTS AS IT
TRANSITIONS INTO AN EXTRATROPICAL CYCLONE.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN OVERALL GOOD
AGREEMENT REGARDING THE TRACK OF 19W, ESPECIALLY OVER THE NEXT 72
HOURS. HOWEVER, AFTER TAU 72, THE ALONG TRACK SPREAD INCREASES
SIGNIFICANTLY. THE COMBINATION OF GALWEM AND UKMET MAKE UP THE
SLOWEST MEMBERS AND GFS MAKES UP THE FASTEST MEMBER. THE JTWC TRACK
IS PLACED BETWEEN THE TWO SCENARIOS CLOSER TO CONSENSUS WITH HIGH
CONFIDENCE THROUGH TAU 72 AND MEDIUM THEREAFTER. INTENSITY GUIDANCE
IS IN MODERATE AGREEMENT WITH AGREEMENT ON STAGNANT INTENSITY
THROUGH TAU 36 AND GRADUAL INTENSIFICATION AFTERWARDS. THE PEAK
INTENSITY RANGES FROM 50 KTS (HAFS-A) AND 70 KTS (COAMPS-TC GFS
BASED). THE JTWC INTENSITY FORECAST PEAK IS PLACED IN THE MIDDLE AT
60 KTS NEAR TAU 96. MODELS ALSO AGREE ON WEAKENING AFTER TAU 96.
OVERALL, THE JTWC INTENSITY FORECAST IS PLACED WITH MEDIUM
CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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